Most of the undoped conjugated conducting polymers have wide energy gaps between the valence and conduction bands, which range from 1.5 to 3.0 eV. After conducting polymers having been doped, new energy states are developed within the band gap and the polarons and bipolarons are formed to lower the energy barriers and enhance the conductivities of the conjugated conducting polymers. Polyisothianaphthene (PITN) was firstly electrochemically synthesized and reported in 1984 by Wudl and Heeger et al. They obtained a band gap of 1.1 eV, which is the lowest band gap of organic polymers being disclosed in the art. At a neutral state, the conductivity of the PITN is about 10.sup.-2 S/cm.sup.2, and the PITN is quite stable in air. After PTIN being doped, the conductivity can reach a higher value of 50 S/cm2. In the meantime, the PITN changes its color from blue into colorless transparence or pale yellow. If the PITN polymer is doped by an electrochemical process, it will possess a reversible electrochromic property. The so-called "electrochromic property" is obtained firstly by utilizing a conducting polymer as a working electrode in a specific medium of an ion salt, and then applying a positive voltage between the working electrode and a counter electrode to electrochemically dope the working electrode. Two new energy states are developed between the valence and conduction bands. In other words, polarons and bipolarons are formed. Then a new peak at the region of low energy (or long wavelength) in the absorption spectrum for the conducting polymer is found. The intensity of the absorption peak in the original region decreases with the increase of the degree of doping whereas the intensity of the absorption in the new-formed low energy region increases. The phenomenon results in the color change of the PITN polymer. Therefore, when a PITN polymeric material, which is originally blue, is doped in an electrochemical reaction cell containing an electrolyte solution by applying a proper voltage thereto, the PITN will become colorlessly transparent or palely yellow. If a proper reversed voltage is applied, the PITN will change back into blue. When a voltage within a specific range is applied to the PITN, the electrochromic property is reversible. This is the reason why the PITN is utilized to fabricate electrochromic display (ECD) devices with sharp contrasts and sinart windows.
A traditional electrochromic display device contains a transparent conducting glass coated thereon an electrochromic conducting polymeric film as an anode, a metal sheet as a cathode, and an appropriate liquid or polymeric electrolyte as an electrolyte. When a proper voltage is applied between the anode and the cathode to proceed doping or dedoping, the color of the electrochromic conducting polymeric film can be controlled thereby. If a smart window is to be fabricated, a transparent conducting material has to be utilized as the cathode instead of the metal plate for light permeability. In general, the conventional conducting polymers utilized to manufacture ECDs, compared to liquid crystal displays (LCDs), have advantages of being able to be formed and adopted in large area without blind visual angle, but have shortages of slow response time, e.g. about 100 milliseconds for changing colors thereof. However, this response time is acceptable for a smart window. The response time of PITN is about 10 milliseconds and is faster than conventional conducting polymers, and the contrast between color changes of PITN is remarkable. Moreover, PITN has a capability of maintaining heat energy. For example, at day time in winter, transparent PITN film is permeable to the radiant heat from sun, and the temperature in a room can be raised by the incident sun light. At night, PITN film of a dark color prevents heat from escaping from a room in the form of infrared ray when the surroundings are at lower temperatures. The energy consumption is reduced. Therefore, the smart windows utilizing electrochromic PITN can also be called electrochromic thermal windows. Owing to the versatility of PITN, it is valuable to further apply PITN to various applications such as a coating material on anodes or cathodes of batteries and on the electrodes of the solar cells. Being utilized to manufacture a device, PITN has to be fabricated in the form of a film or a membrane. Most prior art adopts the electrochemical method to produce PITN films.
As mentioned in the foregoing, the first reported method for synthesizing PITN was presented by Wudl and Heeger et al. in 1984. Up to now, there are a large number of the related methods being developed. Let's have an overall review of those various published papers and disclosures as follows.
1. Polymerization of isothianaphthene (ITN):
a) Electrochemical method:
A PITN film is deposited on a working electrode by introducing ITN as a monomer into a solution of acetonitrile (ACN) in a reaction cell, adding tetraphenyl phosphorium salt as a conducting electrolyte therein, utilizing a conducting indium tin oxide glass plate or a platinum plate as a working electrode and another platium plate as a counter electrode, and then applying a proper current and voltage between the working and counter electrodes.
b) Photopolymerization method:
A PITN film is deposited on a glass by the irradiation of a 500W Xe light after the steps of introducing ITN as a monomer into an ACN solution in a reaction cell, adding tetrabutylammonium bromide as an electrolyte and carbon tetrachloride as an electron-pair acceptor therein, and immersing therein the glass.
c) Elimination of hydrogen from precursor of PITN:
PITN powders can be obtained by adopting methyl sulfonic acid as a cationic catalyst to polymerize ITN into poly(1,3-dihydroisothianaphthene) (PDHITN) in an anhydride dichloromethane solution, and then eliminating hydrogen in the back-bone from PDHITN by SO.sub.2 Cl.sub.2 as a dehydrogenation agent.
d) Direct polymerization of ITN:
Powdered PITN precipitate is obtained by milizing 7,7,8,8-tetracyanoquinodimethane (TCNQ), H.sub.2 SO.sub.4, AlCl.sub.3, or CuCl.sub.2 as an oxidant to oxidatively polymerize ITN.
2. Polymerization of 1,3-dihydroisothianaphthene (DHITN):
a) Electrochemical polymerization:
A PITN film is deposited on a working electrode by introducing DHITN as a monomer into an ACN solution containing tetraethylammonium tetrafluoroborade (Et.sub.4 NBF.sub.4), tetrabutylammonium tetrafluoroborade (Bu.sub.4 NBF.sub.4), or tetrabutylammonium hexafluorophosphate (Bu.sub.4 NPF.sub.6) as a conducting electrolyte, immersing an conducting indium tin oxide glass plate as a working electrode and a platium plate as a counter electrode therein, and applying a proper current and potential.
b) Chemical preparation:
PITN powders are obtained by adopting dry nitromethane as a solvent and introducing PITN as a monomer and FeCl.sub.3 of the same equivalent therein under an environment of 50.degree. C. in air, e.g. in the presence of oxygen.
3. Polymerization of 1,3-dihydroisothianaphthene-2-oxide (DHITNO):
a) PITN powders are obtained by polymerizing DHITNO in the presence of an oxidant of H.sub.2 SO.sub.4 or a mixture of H.sub.2 SO.sub.4 and CH.sub.2 Cl.sub.2.
b) PITN powders are obtained by polymerizing DHITNO in the presence of an oxidant of n-chlorosuccinimide (NCS).
4. Polymerization of ITN with a long side chain:
This method includes steps of synthesizing a derivative of ITN with a long alkyl side chain or a heterocyclic compound similar to ITN as a monomer, polymerizing the monomer in chloroform in the presence of an oxidant of FeCl.sub.3 and dry air at 50.degree. C., dedoping the polymer in a hydrazine aqueous solution, precipitating the dedoped PITN in the form of black powders in methyl alcohol, and then dissolving the obtained black powders in chloroform to eliminate low molecular weight polymers (i.e., oligomers, whose molecular weights are less than 3500) therefrom by a dialysis process to obtain a product of either poly(5-decylisothianaphthene) (referred as Product I thereinafter) or poly(2,3-dihexylthieno- 3,4-b!pyrazine) (referred as Product II thereinafter) of dark blue or black high molecular weight powders. The product obtained thereby is further dissolved in an ordinary solvent, such as chloroform, to deposit a film on a substrate. Pomerantz et al. (J. Chem. Soc., Chem. Commun., 1672 (1992)) disclosed the processes for synthesizing and polymerizing the monomers of Product II. The monomers and the polymers of Product I are respectively shown as follows: ##STR1## and the monomers and the polymers of Product II are respectively shown as follows: ##STR2##
5. U.S. Pat. No. 4,789,748 (1988) issued to K-Y. Jen et al. discloses a process for polymerizing 1,3-dihydroisothianaphthene (DHITN) in nitromethane in the presence of oxygen.
6. U.S. Pat. No. 4,772,940 (1988) issued to F. Wudl et al. discloses (1) an electrochromic display (ECD) comprising a main device of a PITN film grown on a transparent conducting medium as a working electrode by an electrochemical polymerization process wherein the film thickness of the PITN is ranged from 0.03-30 .mu.m; (2) a PITN polymer being reversible for doping and dedoping processes wherein the structures before and after being doped are respectively shown as follows: ##STR3## wherein either one of R.sub.1 and R.sub.2 is H, C.sub.m H.sub.2m+1 (m=1-5), OCH.sub.3, or SCH.sub.3, X is S, Se, or Te, Y.sub.- is ClO.sub.4.sup.-, BF.sub.4.sup.-, PF.sub.6.sup.-, AsF.sub.6.sup.-, SbF.sub.6.sup.-, AlCl.sub.4.sup.-, AlBr.sub.4.sup.-, FeCl.sub.4 --, CF.sub.3 SO.sub.3 --, or HSO.sub.4 --, Z=0.01-1, and n=5-500; (3) the solvent for manufacturing ECDs is a non-water solvent of a high dielectric constant, the concentration of the ion salt therein is ranged from 0.0001-10 mole/L, and the distance between two electrodes is 0.05-5 mm; (4) PITN is used for a coating material on the anode of the battery; and (5) the doped transparent PITN film is utilized as the surface electrode of the solar cell.
7. U.S. Pat. No. 4,795,242 (1989) issued to F. Wudl et al. discloses (1) a process for producing derivatives of the PITN which contains an oxygen atom on a side chain and is capable of alleviating the instability of highly doped PITN polymers; and (2) an electrochemical process for polymerizing the monomers of the derivatives into a polymeric film. The structures of the obtained undoped and doped derivatives of the PITN family are respectively as follows: ##STR4## wherein R.sub.1 is H, C.sub.m H.sub.2m+1 (m=1-8), OCH.sub.3, or SCH.sub.3, R.sub.2 is H or C.sub.m H.sub.2m+1 (m=1-8), X is S, Se, or Te, Y.sup.- is ClO.sub.4.sup.-, BF.sub.4.sup.-, PF.sub.6.sup.-, AsF.sub.6.sup.-, SbF.sub.6.sup.-, AlCl.sub.4.sup.-, AlBr.sub.4.sup.-, FeCl.sub.4.sup.-, CF.sub.3 SO.sub.3.sup.-, or HSO.sub.4.sup.-, Z=0.01-1, and n=5-500.
8. Jap. Pat. No. 62,292,855 (1987) issued to T. Shinsuke et al. discloses a process for polymerizing ITN monomers to obtain transparent conducting PITN composite film incorporated with PVC, which includes steps of utilizing a PVC coated platinum plate as a working electrode, immersing the plate in an ACN solution containing ITN monomers and applying a current density of 5 mA/cm.sup.2 to the solution.
9. Jap. Pat. No. 63,196,622 (1988) issued to U. Novuo et al. discloses an electrochemical process for the dehydrogenation of PDHITN in a solution containing Bu.sub.4 NBr and CH.sub.2 Cl.sub.2, by which PITN powders are obtained.
10. Eur. Pat. Appl. EP 269,090 (1988) issued to S. Toshiyuki et al. discloses a method for producing a transparent PITN film, which includes steps of synthesizing a PITN film on an electrode by an electrochemical process and then electrochemically doping the electrode in a polyphosphoric acid of 0.1 mole/mole-monomer unit. The transparency of the obtained PITN film can be preserved for over 30 days in argon.
11. Jap. Pat. No. 63,215,772 (1988) issued to S. Toshiyuki et al. discloses a method for producing a transparent conducting composite film, which includes steps of electrochemcially polymerizing ITN on a conducting ITO glass to grow a PITN film on an electrode, dedoping the polymerized PITN film, immersing the dedoped PITN film into a vinyl sulfuric acid aqueous solution, treating the resulting solution with an ultrasonic oscillator and, after being taken out from the aqueous solution, irradiating the film with a long-wavelength UV in air for 5 minutes. Then, a composite film is obtained, and the obtained composite film is electrochemically doped in an ACN solution containing Et.sub.4 NClO.sub.4. The produced transparent composite film can keep its transparency and colorlessness for over 50 days in air.
12. Jap. Pat. No. 02,258,833 (1990) issued to F. Eiji discloses a method for producing a stable suspended PITN aqueous dispersion by oxidatively polymerizing ITN derivatives in the presence of anionic polymers and/or anionic surfactants, in which a FeCl.sub.3 solution is dropwisely added to the ITN derivatives. The obtained PITN suspension solution is dialyzed to obtain a solution which is stable when stored at 5.degree. to 20.degree. C. for 3 months. Furthermore, the obtained dispersion is blended with a poly(vinyl acetate) emulsion and is deposited on a glass plate and dried to give a PITN and PVC composite film with light transmission of about 30% and conductivity of about 10.sup.-4 S/cm.
13. Jap. Pat. No. 02,258,832 (1990) issued to F. Eiji discloses a method for producing a stable suspended PITN aqueous dispersion similar to the method previously described but in the presence of cationic, nonionic, anionic and amphoteric polymers and/or cationic, nonionic and amphoteric surfactants instead. The obtained PITN suspension solution is stable when stored at 5.degree. to 20.degree. C. for 3 month. Furthermore, the obtained dispersion is blended with a poly(vinyl acetate) emulsion and is deposited on a glass plate and dried to give a PITN and PVC composite film with conductivity of about 10.sup.-3 S/cm.
14. Jap. Pat. No. 02,252,726 (1990) issued to F. Eiji discloses an electrochemical polymerization method for polymerizing ITN monomers each of which has a substitutional group containing at least 8 carbon atoms thereon in an ACN solution containing Bu.sub.4 N.sub.4 Cl to obtain a PITN film of 10.sup.-2 S/cm. The obtained PITN film can be dissolved in the ordinary solvent for further processing.
15. Jap. Pat. No. 02,252,727 (1990) issued to F. Eiji discloses another electrochemical polymerization for polymerizing 5-cyanobenzo c!thiophene monomers in an ACN solution containing Bu.sub.4 N.sub.4 Cl to obtain a polymer film with conductivity of 10.sup.-2 S/cm and light transmission of 30%, and the light transmission is further improved to 65% when doped with BuN.sub.4 ClO.sub.4. In comparison with a conventional PITN film similarly prepared, whose light transmission before and after doping are 10% and 40 respectively, the light transmission is improved due to an electronegative substitution group existing in the monomer and polymer of 5-cyanobenzo c!thiophene.
16. Jap. Pat. No. 02,193,120 (1990) issued to O. Ryuichi discloses an electrochemical polymerization and a doping process to obtain transparent PITN films for manufacturing the conducting electrodes of liquid crystal displays (LCDs).
PITN, when utilized to manufacture the electrochromic electrodes of the electrochromic displays or the anodes of batteries, has to be produced in the form of thin film. The processes for producing films will profoundly affect the qualities for further applications. Those presently known processes can be categorized and commented as follows:
1. Electrochemical method: This method has advantages of rapid polymerization and good adhesion to the substrate, however, there are still several shortages such as (1) the monomers are unstable when polymerized so that accompanying side reactions could occur, e.g. the crosslinking reaction, which results in the obtained PITN film being insoluble in an ordinary solvent, (2) highly concentrated monomers are required for the polymerization and a very low degree of polymerization can be achieved, and (3) it is difficult to produce a polymeric film with a large area and a uniform thickness due to the limitations of the polymerization equipments.
2. Photochemical method: This method is capable of depositing a film on any ordinary transparent substrate by a simple equipment, however, there will be structural defects of about 9% upon polymerization and the yield of polymerization is very low.
3. Suspension polymerization method: This method is capable of forming stable suspended PITN in an aqueous phase without any pollution problem; however, it is feasible only to produce composite films and takes much time to proceed a dialysis to purify the obtained PITN solution, and its transparency is unacceptable for further applications.
4. Preparation of a soluble PITN with a long chain substitutional group: This method has advantages of depositing a film on an ordinary film by a simple coating process and the obtained film can be further dissolved by an ordinary solvent. This method, for example disclosed in Jap. Pat. No. 63,215,772 (1988) issued to S. Toshiyuki et al., has its superiority on the processing of PITN films to compete with other methods; however, it is difficult to synthesize long-chain substituted ITN monomers with this method. Moreover, it is necessary to utilize FeCl.sub.3 as the polymerization agent, utilize hydrazine to dedope the obtained solution, and proceed a dialysis step to purify PITN. On the other hand, this method, for example disclosed in Jap. Pat. No. 02,252,726 (1990) issued to F. Eiji, has advantages of obtaining PITN films able to be redissolved in an ordinary solvent; however, it is also difficult to synthesize the long-chain substituted ITN monomers. The monomers have to be polymerized in an electrochemical process, and the yield of polymerization is so low that it causes a high manufacturing costs.
To overcome the above-mentioned shortages and difficulties, a feasible way is to modify the process by eliminating the possibility of forming defects, such as crosslinking, on the obtained film so that it can be soluble in an ordinary solvent for further processing. Based on these considerations, this invention offers a modified process for manufacturing a processable PITN film.